This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. There is a need to determine the physiological significance and molecular characterization of various photoreceptors contained within bacteria. We are studying a putative photoreceptor from Erythobactor litoralis that is thought to play a role in quorum sensing. This 222 amino acid protein contains two domains: an LOV (light, oxygen, and voltage) domain which binds a flavin mononucleotide (FMN) chromophore, and a helix-turn-helix transcription factor domain (LuxR). So far, crystal conditions have been determined and yellow large plate crystals have recently been obtained diffracting to 3.5 Angstroms during a test run at the Swiss Light Source (SLS). In addition to gaining insight about how bacteria respond to their environment in order to maintain life, determining the structure of LOV domain containing proteins can lead to drug design enabling quorum quenching in immuno-compromised individuals.